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Millimeter wave (MMW) phase and delay shifters are used for a variety of applications that include narrowband to broadband, electronically steerable array antenna systems. The system requirements for these antennas have become more stringent and require phase and delay shifters that are power-efficient, have a low insertion loss, are size conservative, and operate over narrow to broad bandwidths. One class of electronic steering means are referred to as phase shifters and this class of electronic steering means is substantially different from the class of electronic steering means that are referred to as delay shifters. The phase shifter steering means, are generally applicable for narrow to moderate bandwidth antenna system applications while the delay shifter steering means are generally utilized in very broadband antenna system applications.
Typically, phase shifter circuits have used PIN diodes or Field Effect Transistors (FETs) as the active switching devices. FETs have gained popularity as microwave (MW) and MMW switches due to their very low current consumption and small size. Although PIN diodes have very fast switching speeds relative to FETs and other switching devices, they require a holding current to maintain the PIN diode in a low loss xe2x80x9conxe2x80x9d state. In a high power antenna array system, PIN diodes may consume a large amount of aggregate bias power to maintain each forward biased PIN diode at a sufficiently low resistance. PIN diodes and the FETs that are used as switches also have junction capacitances that limit their isolation and, hence, their performance for phase shifter applications at MMW frequencies.
For some applications, particularly large MMW receive antennas, microelectromechanical Systems (MEMS) switch technology has become an attractive alternative to implement the necessary switching functions in phase shifter circuits and systems. A MEMS realized switching module consumes nearly zero bias current, which is much less when compared to PIN diode switching modules, and, has significantly better insertion loss performance than the solid-state alternatives. However, MEMS switching devices have significantly lower switching speeds and lower power-handling characteristics compared with their solid-state counterparts, FETs and PIN diodes.
MEMS switches along with the associated components needed for a phase shifter on a chip may require a very large chip-level surface area compared to the area required by solid state switches. Thus phase shifters using current MEMS switch-based technology are prone to be more expensive than other phase shifter approaches and are unable to meet certain space requirements due to their comparatively increased size.
Therefore, it would be advantageous to provide a phase shifter approach, using MEMS technology, that obviates the need for the large amount of chip surface area they currently require. Additionally, it would be advantageous to enable a MEMS technology that enhances power handling capability when compared to the prior art.
A phase shifter is disclosed in which parasitic elements in a microelectromechanical switch (MEMS) are designed and utilized to provide a predetermined phase shift of a signal of interest. In one embodiment, a phase shifter circuit uses three MEMS switching modules, each of which includes first and second predetermined reactances. The first predetermined reactance is in an electrically parallel configuration with a second predetermined reactance that is in series with an ideal switch. The second reactance is selected to be less than the first reactance, at the center frequency of the signal of interest. The three MEMS switching modules are configured such that a high pass/low pass phase shifter topology can be implemented with the appropriate orientation of the ideal switches.
A phase shifter is disclosed in which parasitic elements in a microelectromechanical system (MEMS) switch are designed and utilized to provide a predetermined phase shift. In one embodiment, a circuit containing three MEMS switching modules, each of which includes a pair of series-coupled reactances is described. The first reactance is determined by an inductor, the second by a capacitor representing the MEMS switch contact in either the up or down positions, and wherein the capacitive reactance is greater than the inductive reactance for the MEMS switch contact in the up position and less than the inductive reactance for the MEMS switch in the down position. The three MEMS switching modules are configured such that a switched high pass/low pass phase shifter topology can be realized with the appropriate actuation of the MEMS switch contacts.
In another embodiment, two MEMS switching modules, that include two series-coupled reactances, are coupled via tuning stubs, each having a predetermined electrical length, to a main transmission line. The first reactance is determined by an inductor, the second by a capacitor representing the MEMS switch contact in either the up or down positions, and wherein the capacitive reactance is greater than the inductive reactance for the MEMS switch contact in the up position and less than the inductive reactance for the MEMS switch in the down position. Each of the two tuning stubs is coupled to the main transmission line in a spaced apart configuration having a predetermined electrical distance from one another.